Method for the production of cysteine hydrochloride



, 2,907,703 Patented Oct. 6, 1959 No Drawing. Application November 2, 1956 Serial No. 619,938

Claims priority, application Germany November 29, 1955 8 Claims, (Cl. 204-73) This invention relates to cysteine hydrochloride and a method for producing the same. More in particular, this invention relates to a method of producing cysteine hydrochloride electrolytically and to cysteine hydrochloride produced by this method.

n It is known in the art to produce cysteine hydrochloride by the reduction ofcystine with hydrogen in statu nascendi obtained by letting hydrochloric acid react upon non-precious metals, primarily zinc, aluminum and tin. Especially tin has proved to be very suitable for use as a hydrogen producer in this process because it can be easily removed in the form of its sulfidefrom the reaction solution.

However, this process is quite expensive because the metals used albeit non-precious, are still comparatively costly. In addition, the yield as well as the degree of purity of the final product is unsatisfactory.

On the other hand it is not feasible to carry out the reductive process catalytically. A substantial or even total desulfurization would be the inevitable result.

It is, therefore, an object of the present invention to provide a method of producing cysteinehydrochloride whereby a greater yield of the end product can be obtained than according to known processes/,3; 1

It is another object of th -invention to provide a method of producing cysteine hydrochloride whereby an end product having ahigher degree of purity can be obtained than under any of the known processes. It is a further object of the present invention to provide a method of producing cysteine hydrochloride which is less compli cated and more economical than any of the methods known in the art.

It is finally an object of the invention to provide a cysteine hydrochloride having a particularly high degree of purity.

These objects of the invention are achieved and the disadvantages of conventional methods of producing cysteinehydrochloride are avoided by reducing cystine electrolytically. This can be done without a preliminary treatment of the electrodes if the latter consist of a material which enters into an intermediary reaction with cystine. The electrodes may be made of nickehcopper and other known electrode metals. According to a preferred embodiment of the invention, however, a tin cathode is employed. In this case a current yield of 100% is assured. If copper cathodes are used, the current yield attains only 89% and in the case of nickel cathodes the yield reaches only 30%. i i

If the electrolytic process according to. the invention is carried out with a current density at a cathode of 0.05 amp/cm. and a voltage at the" electrodesxof '8-10 volts, and the reaction solution is caused to "boil, .a practically quantitative yield of a pure, white cysteinehydrochloride is obtained. n g

If a tin cathode is used, theelectrode is converted to a tin sponge during the electrolysis. This is the result of an intermediary reaction of the tin with the cystine and a subsequent separation ofthe intermediary compound formed thereby. Therefore, if a proper progress of the United States Patent Ofiice electrolysis is to be maintained, it is necessary to remove the tin sponge and replace the electrode by a new one from time to time. It is, therefore, a particular feature of the invention to employ an'electrode' composed of a metal not capable of reacting with cystine and a tin cover. According to one embodiment of my invention an electrode bearing a tin coating applied prior to the start of the electrolysis, is employed.

According to another, preferred embodiment of the invention, the tin coating on the electrode is produced during the process of the electrolytic reduction itself. As a source for the automatic formation of the tin cathode coating a soluble tin salt is used which is added to the reaction solution in small amounts before the electrolysis begins. Instead of the tin salt, a small amount of elementary tin may be added to the solution. This can be done by introducing a tin bar into the receptacle during the electrolysis, without connecting this tin bar with the electrodes. Since, according to this arrange ment, the cathode can be made of a material retaining its structure during the process, such as for example nickel or silver, and as the necessary amount of tin can be limited to a very small percentage, the annoying formation of sludge is largely suppressed and the hitherto resulting interruptions of the process are, therefore,

i avoided.

. time the solution is also free from tin ions.

ginning ofthe electrolysis, a spongy layer of deposited If the process according to the invention just described is employed, the electrolysis proceeds without interruption and without requiring any substantial supervision and maintenance until the cystine has been completely reduced.

The effect of tin and similar metals upon the electrolysis is entirely unexpected. It cannot be compared with the effect of mercury upon amalgamated electrodes, because a simultaneous dissolution and separation of tin at the cathode takes place until the entire amount of ycystinehas been reduced to cysteine. This process is unprecedented and the result is unexpected. The current yield is quantitative.

The manner in which the reaction takes place is surprising, too. The process according to the invention is reference to the following examples, which are, of course,

not to be considered as limiting the scope and the'applicability of the invention.

Example I A cathode consisting of a tin sheet having an effective surface area of approximately 40 cm. and an anode formed by a carbon bar are suspended in a beaker having a capacity of 800 cc. The anode is screened off against the cathode space by a diaphragm. The anode space is now charged with 2 n hydrochloric acid, and into the cathode space a suspension of g. cystine dissolved in 250 cc. hydrochloric acid and 250 cc. water is fed. Hereafter, the electrolysis is started with a current of 2 amperes anti continued until hydrogen develops at the cathode after a period of approximately 13 hours.

After the be tin develops at the cathode which is' constantly growing until the end of theelectrolysis. The solution is then fil- At this tered off and boiled down. 175 g. of crystallized cysteine hydrochloride are obtained.

Example II A cathode consisting of a copper sheet having an effective surface area of approximately 40 cm. and an anode, formed by a carbon bar are suspended in a beaker having a capacity of 800 cc. The anode is screened oif against the cathode space by a diaphragm. The anode space is now charged with 2 n hydrochloric acid, and into the cathode space a suspension of 120 g. cystine dissolved in 250 cc. hydrochloric acid and 250 cc. water is fed. Hereafter, the electrolysis is started with a current of 2 amperes. The development of-hydrogen sets in right at the beginning of the electrolysis. The current yield is therefore correspondingly small. After hours half the reduction is attained. The cathode liquid is then boiled down. 172 grs. of pure cysteine hydrochloride are obtained.

' Example III A cathode consisting of a copper sheet having an effective surface of 40 cm. and an anode formed by a carbon bar and suspended in a beaker having a capacity of 800 cc. The anode is screened off against the cathode space by a diaphragm. The anode space is now charged with 2 n hydrochloric acid and into the cathode space a suspension of 120 g. cystine dissolved in 250 cc. hydrochloric acid and 250 cc. water is fed. Furthermore, 2 grams of tin-(ID-chloride (SnCl are added to this suspension. Hereafter the electrolysis is started with a current of 2 amperes and continued until hydrogen develops at the cathode after a period of approximately 13 hours. At this time, the solution is also free from tin ions. After the commencement of the electrolysis a spongy layer of tin is deposited at the cathode which layer is constantly growing until the end of the electrolysis. The solution is then filtered off and boiled down. 170 to 175 g. of crystallized cysteine hydrochloride are obtained.

Example IV A cathode consisting of a silver cathode having an effective surface of 40 cm. and an anode formed by a carbon bar is suspended in a beaker having a capacity of 800 cc. The anode is screened 01f against the cathode space by a diaphragm. The anode space is now charged with 2 n hydrochloric acid, and into the cathode space a suspen sion of 120 g. cystine dissolved in 250 cc. hydrochloric acid and 250 cc. water is fed. In addition, one gram of metallic tin is added into the suspension, and is dissolved in the same. Hereafter the electrolysis is started with a current of 2 amperes, and continued until, after a period of approximately 13 hours, hydrogen develops at the cathode. At this time the solution is also free from tin ions. After the commencement of the electrolysis, a spongy layer of deposited tin develops at the cathode which layer is constantly growing until the end of the electrolysis. The solution is then filtered and boiled down. 172 to 175 grs. of crystallized cysteine hydrochloride are obtained.

Example V A cathode consisting of a nickel cathode having an effective surface of 40 cm. and an anode formed by a carbon bar is suspended in a beaker having a capacity of 800 cc. The anode is screened off against the cathode space by a diaphragm. The anode space is now charged with 2 n hydrochloric acid, and into the cathode space a suspension of 120 g. cystine dissolved in 250 cc. hydrochloric acid and 250 cc. water is fed. In addition, a strip of tin sheet measuring 10 to 60 min. and having a thickness of 1 to 2 mm. is suspended into the cathode space. Hereafter, the electrolysis is started with a current of '2 amperes, and continued until, after a period of approximately 13 hours, hydrogen develops at the cathode. At

this time the solution is also free from tin ions.

Example VI I A cathode consisting ofa coal bar having an effective surface of 40 cm. and an anode formed by a carbon bar is suspended. The anode is screened off against the cathode space by a diaphragm in a beaker having a capacity of 800 cc. Theianod'e space is now charged with 2 n hydrochloric acid, and into the cathode space a suspen- 'The solution is then filtered and boiled down.

sion of g. cystine dissolved in 250 cc. hydrochloric acid and 250 cc. water is fed. Furthermore, 4 g. of tin chloride dissolved in 20 cc. of water are added to this suspension. Hereafter, the electrolysis is started with a current of 2 amperes, and continued until, after a'period of approximately 13 hours, hydrogen develops at the cathode. At this time the solution is free from tin ions. After the commencement of the electrolysis, a spongy layer of deposited tin develops at the cathode which layer is constantly growing until the' end of the electrolysis. 172 to 175 g. of crystallized cysteine hydrochloride are obtained.

It will be'understood that this invention is susceptible to further modification and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What I claimis:

1. In a process for the production of cysteine salt from cystine by the electrolytic reduction of the latter in a hydrochloric acid solution, the improvement comprised of maintaining a surface'coating of metallic tin on the cathode body.

2. The process of claim 1, wherein the electrolysis is carried out at a current density of from 0.02-0.5 amperes per square centimeter. 3

3. The process of claim 1, wherein the cathode body is made of a metal selected from the group consisting of copper and tin. I r j V 1 V 4. The process of claim 3, wherein the cathode body is made of tin.

5. The process of claim 3, wherein the cathode body is made of copper.

6. The process of claim 3, wherein the cathode body is coated with an electrolytically regeneratable tin coating.

7. In a process for the production of cysteine salt from cystine'by the electrolytic reduction of the latter in a hydrochloric acidsolution, the improvement comprising of the addition of tin chloride to the electrolytic bath, whereby a metallic tin coating is formed on the cathode body during electrolysis.

8. In a process for the production of cysteine salt from cystine by the electrolytic reduction of the latter in a hydrochloric acid solution, the improvement comprising of the addition of metallic tin to the electrolytic bath, where: by a metallic tin coating is formed on the cathode body during electrolysis.

References Cited in the file of this patent Chemical Abstracts, 1948, vol. 42, page 3726(a), Electrolytic Oxidation and Reduction, Glasstone and Hickling pages 188-190, D. Van Nostrand Company, Inc., New York (1936). v 7

Chemical Abstracts, 1954, vol. 48, page 12188(a).

Chemical Abstracts, 1952, vol. 46, page 4597(b).

. Chemical Abstracts, 1948, vol. 42, page 3726(a).' Chemical Abstracts, 1935, .vol. 29, page 7354(1). Chemical Abstracts, 1932, vol. 26, page 3976(3).

. Chemical Abstracts, 1928,1101. 22, page 4137(1). C emical Abstracts, 1924, vol. 18, page 380(3). 

1. IN A PROCESS FOR THE PRODUCTION OF CYSTEINE SALT FROM CYSINE BY THE ELECTROLYTIC REDUCTION OF THE LATTER IN A HYDROCHLORIC ACID SOLUTION, THE IMPROVEMENT COMPRISED OF MAINTAINING A SURFACE COATING OF METALLIC TIN ON THE CATHODE BODY. 